In the performance of loading and unloading operations with respect to railroad hopper cars, the periodic movement of a car, or the sequential positioning of individual cars of a train of coupled cars, either in a forward or backward mode, is essential. For example, all loading and unloading stations are set up so that as one car or section of the car is completed, the next car or section must be moved to receive or discharge its material.
There are several different types of apparatus and methods conventionally employed for accomplishing the foregoing operations, the most common of which utilizes one or more steel cables operatively connected to a rotatable drum. The cable is connected to the railroad car and the same is advanced by rotating the drum through means of a drum motor and transmission mechanism. These systems have generally proven quite complex as the cables must necessarily be routed about sheaves or within conduits or raceways disposed underneath the tracks. In addition, if the cables are disposed above ground, then the same become hazardous obstacles to both machinery and personnel. Still further, the fact that such cables are severaly tensioned during operation serves to present an additional potential hazard to personnel should the cable snap.
In addition to the complexity and safety problems characteristic of the aforementioned cable system, the same are also considerably expensive to install and maintain. Installation techniques utilized in conjunction with such systems necessarily entail the location of the cable drum and motor transmission mechanism at a distance from the track being serviced by such elements in order to provide sufficient clearance between the rail cars and the elements. Furthermore, when the cables are routed underneath the rail tracks within cable troughs or raceways, as aforenoted, the troughs present maintenance problems, and this is true regardless of whether or not the troughs or raceways are open or covered.
Another type of apparatus and method which is conventionally employed for performance of the foregoing operations comprises the disposition of the rail tracks upon a grade which is inclined downwardly toward the loading or unloading station. Wheel chocks are disposed in front of one or more wheels in order to prevent forward movement of the rail car or cars, and the same are removed in order to permit the car or cars to advance forwardly. This mode of operation is necessarily performed many times during a hopper car loading operation, and in addition, is quite hazardous due to the fact that the laden rail cars sometimes jump over or push aside the chocks and roll free.
Car type jacks have been conventionally employed for many years in order to move rail cars. In using such apparatus, jacks are interposed between a wheel of the car and the track. The rail car is moved forwardly by means of a person exerting a downward force upon the lever arm of the jack. In some cases, this method is used to overcome the static friction of the wheels of the car at rest on a grade bed; the operator jumping on the car to use the brake. In other cases, this method of operation serves to move the car several inches at a time. Consequently, such a mode of operation must be repeated numerous times in order to advance a car a considerable distance. As can be realized, either of these modes of operation is quite dangerous. This is particularly true if the operator slips or falls, and considering the operative characteristics of such apparatus, the likelihood of such occurring is seen to be considerable.
Hydraulically activated mechanisms for moving railroad cars have also been conventionally employed, and the same normally comprise hydraulic cyclinders which are disposed along the track rails and which energize dogs which move the cars in a forward mode. The operative disadvantages of such apparatus are: (1) the mechanism can only move the cars forwardly, (2) the dogs sometimes slip from engagement unexpectedly releasing the rail car, (3) the lifting force of the dogs tends to derail empty cars, and (4) there is no means for retarding the movement of the cars. In addition, the regions of the track bed within which the hydraulic cylinders are located must be constantly maintained and cleaned in order to prevent the mechanisms from fouling, and consequently, the installation or employment of such apparatus is somewhat limited. For example, such apparatus could not be readily employed within coke plants or other establishments where material spillages normally occur.